Ion-sensitive hard water dispersible polymers and applications therefor

ABSTRACT

The present invention is directed to ion-sensitive, hard water dispersible polymers. The present invention is also directed to a method of making ion-sensitive, hard water dispersible polymers and their applicability as binder compositions. The present invention is further directed to fiber-containing fabrics and webs comprising ion-sensitive, hard water dispersible binder compositions and their applicability in water dispersible personal care products.

The present application is a continuation application of U.S. Pat.application Ser. No. 10/071,640 filed on Feb. 7, 2002, now U.S. Pat. No.6,630,558, which is a divisional application of U.S. patent applicationSer. No. 09/223,999, filed on Dec. 31, 1998, now U.S. Pat. No.6,423,804.

FIELD OF THE INVENTION

The present invention is directed to ion-sensitive, hard waterdispersible polymers. The present invention is also directed to a methodof making ion-sensitive, hard water dispersible polymers and theirapplicability as binder compositions. The present invention is furtherdirected to fiber-containing fabrics and webs comprising ion-sensitive,hard water dispersible binder compositions and their applicability inwater dispersible personal care products.

BACKGROUND OF THE INVENTION

For many years the problem of disposability has plagued industries,which provide disposable diapers, wet wipes, incontinent garments andfeminine care products. While much headway has been made in addressingthis problem, one of the weak links has been the inability to create aneconomical coherent fibrous web, which will readily dissolve ordisintegrate in water, but still have in-use strength. See, for example,U.K. patent disclosure 2,241,373 and U.S. Pat. No. 4,186,233. Withoutsuch a product, the ability of the user to dispose of the product byflushing it down the toilet is greatly reduced, if not eliminated.Furthermore, the ability of the product to disintegrate in a landfill isquite limited because a large portion of the product components, whichmay well be biodegradable or photode-gradable, are encapsulated in orbound together by plastic which degrades over a long period of time, ifat all. Accordingly, if the plastic disintegrated in the presence ofwater, the internal components could degrade as a result of the ruptureof the plastic encapsulation or binding.

Disposable diapers, feminine care products and adult incontinent careproducts usually comprise a body side liner which must rapidly passfluids, such as urine or menses, so that the fluid may be absorbed by anabsorbent core of the product. Typically, the body side liner is acoherent fibrous web, which desirably possesses a number ofcharacteristics such as softness and flexibility. The fibrous web of thebody side liner material is typically formed by wet or dry (air) layinga generally random plurality of fibers and joining them together to forma coherent web with a binder. Past binders have preformed this functionwell. From an environmental standpoint, it might be stated that the pastbinders have performed this function too well in that the binders tendednot to degrade and thus the liner remained intact, severely hamperingany environmental degradation of the disposable product.

Recent binder compositions have been developed which are moreenvironmentally responsible and exhibit better water solubility thanpast binders. One class of binders includes polymeric materials havinginverse solubility in water. These binders are insoluble in warm water,but are soluble in cold water, such as found in a toilet. It is wellknown that a number of polymers exhibit cloud points or inversesolubility properties in aqueous media. These polymers have been citedin several publications for various applications, including (1) asevaporation retarders (JP 6207162); (2) as temperature sensitivecompositions, which are useful as temperature indicators due to a sharpcolor change associated with a corresponding temperature change (JP6192527); (3) as heat sensitive materials that are opaque at a specifictemperature and become transparent when cooled to below the specifictemperature (JP 51003248 and JP 81035703); (4) as wound dressings withgood absorbing characteristics and easy removal (JP 6233809); and (5) asmaterials in flushable personal care products (U.S. Pat. No. 5,509,913,issued to Richard S. Yeo on Apr. 23, 1996 and assigned to Kimberly-ClarkCorporation).

Other recent binders of interest include a class of binders, which areion-sensitive. Several U.S. and European patents assigned to LionCorporation of Tokyo, Japan, disclose ion-sensitive polymers comprisingacrylic acid and alkyl or aryl acrylates. See U.S. Pat. Nos. 5,312,883;5,317,063; and 5,384,189; as well as, European Patent No. 608460A1. InU.S. Pat. No. 5,312,883, terpolymers are disclosed as suitable bindersfor flushable nonwoven webs. The disclosed acrylic acid-basedterpolymers, which comprise partially neutralized acrylic acid, butylacrylate and 2-ethylhexyl acrylate, are suitable binders for use influshable nonwoven webs in some parts of the world. However, because ofthe presence of a small amount of sodium acrylate in the partiallyneutralized terpolymer, these binders fail to disperse in watercontaining more than about 15 ppm Ca²⁺ and/or Mg²⁺. When placed in watercontaining more than about 15 ppm Ca²⁺ and/or Mg²⁺ ions, nonwoven websusing the above-described binders maintain a tensile strength greaterthan 30 g/in, which negatively affects the “dispersibility” of the web.The proposed mechanism for the failure is that each calcium ion bindswith two carboxylate groups either intramolecularly or intermolecularly.Intramolecular association causes the polymer chain to coil up, whicheventually leads to polymer precipitation. Intermolecular associationyields crosslinking. Whether intramolecular or intermolecularassociations are taking place, the terpolymer is not soluble in watercontaining more than about 15 ppm Ca²⁺ and/or Mg²⁺. Due to the stronginteraction between calcium ions and the carboxylate groups of theterpolymer, dissociation of the complex is highly unlikely because thisassociation is irreversible. Therefore, the above-described polymer thathas been exposed to a high Ca²⁺ and/or Mg²⁺ concentration solution forabout 8 hours or more will not disperse in water even if the calciumconcentration decreases. This limits the application of the polymer as aflushable binder material because most areas across the U.S. have hardwater, which contains more than 15 ppm Ca²⁺ and/or Mg²⁺.

Although many patents disclose various ion and temperature sensitivecompositions for flushable materials, there exists a need for flushableproducts possessing softness, three dimensionality, and resiliency;wicking and structural integrity in the presence of body fluids at bodytemperature; and true fiber dispersion after toilet flushing so thatfibers do not become entangled with tree roots or at bends in sewerpipes. Moreover, there is a need in the art for flushable productshaving water-dispersibility in all areas of the world, including softand hard water areas. Such a product is needed at a reasonable costwithout compromising product safety and environmental concerns,something that past products have failed to do.

SUMMARY OF THE INVENTION

The present invention is directed to ion-sensitive polymers, which havebeen developed to address the above-described problems associated withcurrently available, ion-sensitive polymers and other polymers describedin literature. The ion-sensitive polymers of the present invention havea “trigger property,” such that the polymers are insoluble in high saltsolutions, but soluble in low salt solutions, including hard water.Unlike some ion-sensitive polymers, which lose dispersibility in hardwater because of ion cross-linking by calcium ions, the polymers of thepresent invention are relatively insensitive to calcium and/or magnesiumions. Consequently, flushable products containing the polymers of thepresent invention maintain dispersibility in hard water.

The polymeric materials of the present invention are useful as bindersand structural components for air-laid and wet-laid nonwoven fabrics forapplications such as body-side liner, fluid distribution material, fluidin-take material (surge) or cover stock in various personal careproducts. The polymeric materials of the present invention areparticularly useful as a binder material for flushable personal careproducts such as diapers, feminine pads, panty liners, and wet wipes.The flushable products maintain integrity during storage and use, andbreak apart after disposal in the toilet when the salt concentrationfalls below a critical level.

The present invention also discloses how to make water-dispersiblenonwovens, including coverstock (liner), intake (surge) materials andwet wipes, which are stable in fluids having high ionic content, usingthe above-described unique polymeric binder compositions. The resultantnonwovens are flushable and water-dispersible due to the tailored ionsensitivity, which is triggered regardless of the hardness of waterfound in toilets throughout the United States and the world.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to be an effective ion triggerable material suitable for use influshable personal care products, the material should desirably be (1)functional, i.e., maintain wet strength under controlled conditions anddissolve or disperse rapidly in soft or hard water such as found in atoilets and sinks around the world; (2) safe (not toxic); and (3)economical. The ion-sensitive polymers of the present invention meet theabove criteria.

Unlike the Lion polymers and other polymers cited in technicalliterature, the polymers of the present invention are ion triggerable,as well as, soluble in water having from greater than about 15 ppm Ca²⁺and/or Mg²⁺ to about 200 ppm Ca²⁺ and/or Mg²⁺. The polymers of thepresent invention have been formulated to minimize the potentiallystrong interaction between the anions of the polymers and the cations inthe water. This strong interaction can be explained via the hard-softacid-base theory proposed by R. G. Pearson in the Journal of theAmerican Chemical Society, vol. 85, pg. 3533 (1963); or N. S. Isaacs inthe textbook, Physical Organic Chemistry, published by LongmanScientific and Technical with John Wiley & Sons, Inc., New York (1987).Hard anions and hard cations interact strongly with one another. Softanions and soft cations also interact strongly with one another.However, soft anions and hard cations, and vice-versa, interact weaklywith one another. In the Lion polymers, the carboxylate anion of thesodium acrylate is a hard anion, which interacts strongly with the hardcations, Ca²⁺ and/or Mg²⁺, present in moderately hard and hard water. Byreplacing the carboxylate anions with a softer anion, such as asulfonate anion, the interaction between the anions of anion-triggerable polymer and the hard cations, Ca²⁺ and/or Mg²⁺, presentin moderately hard and hard water, is reduced.

The polymers of the present invention are formed from one or moremonomers such that the resulting polymer has a “hydrophobic/hydrophilicbalance” throughout the polymer chain. As used herein, the term“hydrophobic/hydrophilic balance” refers to a balance of hydrophobic andhydrophilic moieties having a controlled degree of hardness or softness,as discussed above, along the polymer chain, which results in a polymerhaving a desired trigger property in soft, moderately hard, or hardwater. As used herein, the term “soft water” refers to water having adivalent ion content of less than about 10 ppm. As used herein, the term“moderately hard water” refers to water having a divalent ion content offrom about 10 to about 50 ppm. As used herein, the term “hard water”refers to water having a divalent ion content of more than about 50 ppm.By controlling the hydrophobic/hydrophilic balance and the compositionof the polymer, ion-sensitive polymers having desired in-use bindingstrength and water-dispersibility in hard water are produced.

The polymers of the present invention may comprise any vinyl monomerscapable of free radical polymerization. At least a portion of theresulting polymer comprises one or more monomer units having ahydrophobic moiety thereon and one or more monomer units having ahydrophilic moiety thereon. Suitable monomers, which provide a degree ofhydrophobicity to the resulting polymer include, but are not limited to,vinyl esters, such as vinyl acetate; alkyl acrylates; acrylonitrile;methacrylonitrile; and vinyl chloride. Suitable monomers, which providea degree of hydrophilicity to the resulting polymer include, but are notlimited to, acrylamide and methacrylamide based monomers, such asacrylamide, N,N-dimethyl acrylamide, N-ethyl acrylamide, N-isopropylacrylamide, and hydroxymethyl acrylamide; N-vinylpyrrolidinone;N-vinylforamide; hydroxyalkyl acrylates and hydroxyalkyl methacrylates,such as hydroxyethyl methacrylate and hydroxyethyl acrylate; andmonomers containing one or more of the following functional groups:hydroxy, amino, ammonium, sulfonate, ether, carboxylate, carboxylicacid, amide, and sulfoamide groups. Other suitable hydrophilic aridhydrophobic monomers include the vinyl monomers disclosed in U.S. Pat.No. 5,317,063, assigned to Lion Corporation, Tokyo, Japan, which isherein incorporated by reference in its entirety.

The amount of hydrophobic monomer used to produce the ion-sensitivepolymers of the present invention may vary depending on the desiredproperties in the resulting polymer. Desirably, the mole percent ofhydrophobic monomer in the ion-sensitive polymer is up to about 70 mol%. More desirably, the mole percent of hydrophobic monomer in theion-sensitive polymer is from about 15 to about 50 mol %. Mostdesirably, the mole percent of hydrophobic monomer in the ion-sensitivepolymer is from about 25 to about 40 mol %.

The ion-sensitive polymers of the present invention may have an averagemolecular weight, which varies depending on the ultimate use of thepolymer. Desirably, the ion-sensitive polymers of the present inventionhave a weight average molecular weight ranging from about 10,000 toabout 5,000,000. More desirably, the ion-sensitive polymers of thepresent invention have a weight average molecular weight ranging fromabout 25,000 to about 2,000,000.

The ion-sensitive polymers of the present invention may be preparedaccording to a variety of polymerization methods, preferably a solutionpolymerization method. Suitable solvents for the polymerization methodinclude, but are not limited to, lower alcohols such as methanol,ethanol and propanol; a mixed solvent of water and one or more loweralcohols mentioned above; and a mixed solvent of water and one or morelower ketones such as acetone or methyl ethyl ketone.

In the polymerization method, any polymerization initiator may be used.Selection of a particular initiator may depend on a number of factorsincluding, but not limited to, the polymerization temperature, thesolvent, and the monomers used. Suitable polymerization initiators foruse in the present invention include, but are not limited to,2,2′-azobisisobutyronitrile, 2,2′-azobis(2-methylbutyronitrile),2,2′-azobis(2,4-dimethylvaleronitrile),2,2′-azobis(2-amidinopropane)dihydrochloride,2,2′-azobis(N,N′-dimethyleneisobutylamidine), potassium persulfate,ammonium persulfate, and aqueous hydrogen peroxide. The amount ofpolymerization initiator may range from about 0.01 to 5 wt % based onthe total weight of monomer present.

The polymerization temperature may vary depending on the polymerizationsolvent, monomers, and initiator used, but in general, ranges from about20° C. to about 90° C. Polymerization time generally ranges from about 2to about 8 hours.

In one embodiment of the present invention, hydrophilic monomers, suchas acrylic acid or methacrylic acid, are incorporated into theion-sensitive polymers of the present invention along with one or moresulfonate-containing monomers. The sulfonate anion of these monomers aresofter than carboxylate anion since the negative charge of the sulfonateanion is delocalized over three oxygen atoms and a larger sulfur atom,as oppose to only two oxygen atoms and a smaller carbon atom in thecarboxylate anion. These monomers, containing the softer sulfonateanion, are less interactive with multivalent ions present in hard water,particularly Ca²⁺ and Mg²⁺ ions. Suitable sulfonate-containing monomersinclude, but are not limited to, sodium salt of styrenesulfonic acid(NaSS), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), sodium saltof 2-acrylamido-2-methyl-1-propanesulfonic acid (NaAMPS), vinylsulfonicacid, and sodium salt of vinylsulfonic acid. To maintain thehydrophobicihydrophilic balance of the ion-sensitive polymer, one ormore hydrophobic monomers are added to the polymer.

In a further embodiment of the present invention, ion-sensitive polymersare produced from four monomers: acrylic acid, AMPS, butyl acrylate, and2-ethylhexyl acrylate. Desirably, the monomers are present inion-sensitive polymer at the following mole percents: acrylic acid,about 50 to less than 67 mol %; AMPS, greater than 0 to about 10 mol %;butyl acrylate, about 15 to about 28 mol %; and 2-ethylhexyl acrylate,about 7 to about 15 mol %. More desirably, the monomers are present inion-sensitive polymer at the following mole percents: acrylic acid,about 57 to about 66 mol %; AMPS, about 1 to about 6 mol %; butylacrylate, about 15 to about 28 mol %; and 2-ethylhexyl acrylate, about 7to about 13 mol %.

In order to further fine tune the hydrophobic/hydrophilic balance of theion-sensitive polymers, at least a portion of the acid moieties, ifpresent, along the polymer chain may be neutralized. For example, theabove-described ion-sensitive polymer comprising four distinct monomersmay be partially or wholly neutralized to convert some or all of theAMPS to NaAMPS. Any inorganic base or organic base may be used as aneutralizing agent to neutralize the acid component of the ion-sensitivepolymers. Examples of neutralizing agents include, but are not limitedto, inorganic bases such as sodium hydroxide, potassium hydroxide,lithium hydroxide and sodium carbonate, and amines such asmonoethanolamine, diethanolaiine, diethylaminoethanol, ammonia,trimethylamine, triethylamine, tripropylamine, morpholine. Preferredneutralizing agents include ethanolamines, sodium hydroxide, potassiumhydroxide, or a combination thereof.

In a further embodiment of the present invention, the above-describedion-sensitive polymers are used as a binder material for flushableand/or non-flushable products. In order to be effective as a bindermaterial in flushable products throughout the United States, theion-sensitive polymers of the present invention remain stable andmaintain their integrity while dry or in high concentrations ofmonovalent and/or multivalent ions, but become soluble in watercontaining up to about 200 ppm Ca²⁺ ions. Desirably, the ion-sensitivepolymers of the present invention are insoluble in a salt solutioncontaining at least about 0.3 weight percent of one or more inorganicand/or organic salts containing monovalent and/or multivalent ions. Moredesirably, the ion-sensitive polymers of the present invention areinsoluble in a salt solution containing from about 0.3 wt % to about 5.0wt % of one or more inorganic and/or organic salts containing monovalentand/or multivalent ions. Even more desirably, the ion-sensitive polymersof the present invention are insoluble in a salt solution containingfrom about 0.5 wt % to about 3.0 wt % of one or more inorganic and/ororganic salts containing monovalent and/or multivalent ions. Suitablemonovalent and/or multivalent ions include, but are not limited to, Na⁺ions, K⁺ ions, Li⁺ ions, NH₄ ⁺ ions, Cl⁻ ions, Ca²⁺ ions, Mg²⁺ ions,Zn²⁺ ions, CO₃ ²⁻ ions, and a combination thereof.

Based on a recent study conducted by the American Chemical Society,water hardness across the United States varies greatly, with CaCO₃concentration ranging from near zero for soft water to about 500 ppmCaCO₃ (about 200 ppm Ca²⁺ ion) for very hard water. To ensure polymerdispersibility across the country, the ion-sensitive polymers of thepresent invention are desirably soluble in water containing up to about50 ppm Ca²⁺ and/or Mg²⁺ ions. More desirably, the ion-sensitive polymersof the present invention are soluble in water containing up to about 100ppm Ca²⁺ and/or Mg²⁺ ions. Even more desirably, the ion-sensitivepolymers of the present invention are soluble in water containing up toabout 150 ppm Ca²⁺ and/or Mg²⁺ ions. Even more desirably, theion-sensitive polymers of the present invention are soluble in watercontaining up to about 200 ppm Ca²⁺ and/or Mg²⁺ ions.

The binder formulations of the present invention may be applied to anyfibrous substrate. The binders are particularly suitable for use inwater-dispersible products. Suitable fibrous substrates include, but arenot limited to, nonwoven and woven fabrics. In many embodiments,particularly personal care products, preferred substrates are nonwovenfabrics. As used herein, the term “nonwoven fabric” refers to a fabricthat has a structure of individual fibers or filaments randomly arrangedin a mat-like fashion. Nonwoven fabrics can be made from a variety ofprocesses including, but not limited to, air-laid processes, wet-laidprocesses, hydroentangling processes, staple fiber carding and bonding,and solution spinning.

The binder composition may be applied to the fibrous substrate by anyknown process of application. Suitable processes for applying the bindermaterial include, but are not limited to, printing, spraying,impregnating or by any other technique. The amount of binder compositionmay be metered and distributed uniformly within the fibrous substrate ormay be non-uniformly distributed within the fibrous substrate. Thebinder composition may be distributed throughout the entire fibroussubstrate or it may be distributed within a multiplicity of smallclosely spaced areas. In most embodiments, uniform distribution ofbinder composition is desired.

For ease of application to the fibrous substrate, the binder may bedissolved in water, or in a non-aqueous solvent such as methanol,ethanol, acetone, or the like, with water being the preferred solvent.The amount of binder dissolved in the solvent may vary depending on thepolymer used and the fabric application. Desirably, the binder solutioncontains up to about 25 percent by weight of binder composition solids.More desirably, the binder solution contains from about 10 to 20 percentby weight of binder composition solids. Plasticizers, perfumes, coloringagents, antifoams, bactericides, surface active agents, thickeningagents, fillers, tackifiers, detackifiers, and similar additives can beincorporated into the solution of binder components if so desired.

Once the binder composition is applied to the substrate, the substrateis dried by any conventional means. Once dry, the coherent fibroussubstrate exhibits improved tensile strength when compared to thetensile strength of the untreated wet-laid or dry-laid substrates, andyet has the ability to rapidly “fall apart”, or disintegrate when placedin soft or hard water having a relatively low monovalent and/ormultivalent ionic concentration and agitated. For example, the drytensile strength of the fibrous substrate may be increased by at least25 percent as compared to the dry tensile strength of the untreatedsubstrate not containing the binder. More particularly, the dry tensilestrength of the fibrous substrate may be increase by at least 100percent as compared to the dry tensile strength of the untreatedsubstrate not containing the binder. Even more particularly, the drytensile strength of the fibrous substrate may be increased by at least500 percent as compared to the dry tensile strength of the untreatedsubstrate not containing the binder.

A desirable feature of the present invention is that the improvement intensile strength is effected where the amount of binder compositionpresent, “add-on”, in the resultant fibrous substrate represents only asmall portion, by weight of the entire substrate. The amount of “add-on”can vary for a particular application; however, the optimum amount of“add-on” results in a fibrous substrate which has integrity while in useand also quickly disperses when agitated in water. For example, thebinder components typically are from about 5 to about 65 percent, byweight, of the total weight of the substrate. More particularly, thebinder components may be from about 10 to about 35 percent, by weight,of the total weight of the substrate. Even more particularly, the bindercomponents may be from about 10 to about 25 percent, by weight, of thetotal weight of the substrate.

The nonwoven fabrics of the present invention have good in-use tensilestrength, as well as, ion triggerability. Desirably, the nonwovenfabrics of the present invention are abrasion resistant and retainsignificant tensile strength in aqueous solutions containing greaterthan about 0.5 weight percent NaCl or a mixture of monovalent andmultivalent ions, wherein the multivalent ion concentration is greaterthan about 500 ppm. Yet the nonwoven fabrics are dispersible in soft tomoderately hard to hard water. Because of this latter property, nonwovenfabrics of the present invention are well suited for disposable productssuch as sanitary napkins, diapers, and dry and premoistened wipes, whichcan be thrown in a flush toilet after use in any part of the world.

The fibers forming the fabrics above can be made from a variety ofmaterials including natural fibers, synthetic fibers, and combinationsthereof. The choice of fibers depends upon, for example, the intendedend use of the finished fabric and fiber cost. For instance, suitablefibrous substrates may include, but are not limited to, natural fiberssuch as cotton, linen, jute, hemp, wool, wood pulp, etc. Similarly,regenerated cellulosic fibers such as viscose rayon and cuprammoniumrayon, modified cellulosic fibers, such as cellulose acetate, orsynthetic fibers such as those derived from polyesters, polyamides,polyacrylics, etc., alone or in combination with one another, maylikewise be used. Blends of one or more of the above fibers may also beused if so desired.

The fiber length is important in producing the fabrics of the presentinvention. In some embodiments such as flushable products, fiber lengthis of more importance. The minimum length of the fibers depends on themethod selected for forming the fibrous substrate. For example, wherethe fibrous substrate is formed by carding, the length of the fibershould usually be at least about 42 mm in order to insure uniformity.Where the fibrous substrate is formed by air-laid or wet-laid processes,the fiber length may desirably be about 0.2 to 6 mm. Although fibershaving a length of greater than 50 mm are within the scope of thepresent invention, it has been determined that when a substantialquantity of fibers having a length greater than about 15 mm is placed ina flushable fabric, though the fibers will disperse and separate inwater, their length tends to form “ropes” of fibers which areundesirable when flushing in home toilets. Therefore, for theseproducts, it is desired that the fiber length be about 15 mm or less sothat the fibers will not have a tendency to “rope” when they are flushedthrough a toilet. Although fibers of various lengths are applicable inthe present invention, desirably fibers are of a length less than about15 mm so that the fibers disperse easily from one another when incontact with water.

The fabrics of the present invention may be formed from a single layeror multiple layers. In the case of multiple layers, the layers aregenerally positioned in a juxtaposed or surface-to-surface relationshipand all or a portion of the layers may be bound to adjacent layers.Nonwoven webs of the present invention may also be formed from aplurality of separate nonwoven webs wherein the separate nonwoven websmay be formed from single or multiple layers. In those instances wherethe nonwoven web includes multiple layers, the entire thickness of thenonwoven web may be subjected to a binder application or each individuallayer may be separately subjected to a binder application and thencombined with other layers in a juxtaposed relationship to form thefinished nonwoven web.

In one embodiment, the fabric substrates of the present invention may beincorporated into cleansing and body fluid absorbent products such assanitary napkins, diapers, surgical dressings, tissues, wet wipes, andthe like. These products may include an absorbent core, comprising oneor more layers of an absorbent fibrous material. The core may alsocomprise one or more layers of a fluid-pervious element, such as fibroustissue, gauze, plastic netting, etc. These are generally useful aswrapping materials to hold the components of the core together.Additionally, the core may comprise a fluid-impervious element orbarrier means to preclude the passage of fluid through the core and onthe outer surfaces of the product. Preferably, the barrier means also iswater-dispersible. A film of a polymer having substantially the samecomposition as the aforesaid water-dispersible binder is particularlywell-suited for this purpose. In accordance with the present invention,the polymer compositions are useful for forming each of theabove-mentioned product components including the layers of absorbentcore, the fluid-pervious element, the wrapping materials, and thefluid-impervious element or barrier means.

The binder formulations are particularly useful for binding fibers ofair-laid nonwoven fabrics. These air-laid materials are useful forbody-side liners, fluid distribution materials, fluid in-take materials,such as a surge material, absorbent wrap sheet and cover stock forvarious water-dispersible personal care products. Air-laid materials areparticularly useful for use as a premoistened wipe. The basis weightsfor air-laid non-woven fabrics may range from about 20 to about 200grams per square meter (gsm) with staple fibers having a 2-3 denier anda length of about 6-15 millimeters. Surge or in-take materials needbetter resiliency and higher loft so staple fibers having about 6 denieror greater are used to make these products. A desirable final densityfor the surge or in-take materials is between about 0.025 grams percubic centimeter (g/cc) to about 0.050 g/cc. Fluid distributionmaterials may have a higher density, in the desired range of about 0.10to about 0.20 g/cc using fibers of lower denier, most desirable fibershave a denier of less than about 1.5. Wipes generally, have a density ofabout 0.05 g/cc to about 0.2 g/cc and a basis weight of about 30 gsm toabout 90 gsm.

One particularly interesting embodiment of the present invention is theproduction of premoistened wipes, or wet wipes, from the above-describedion-sensitive polymers and fibrous materials. For wipes, the nonwovenfabric is, desirably, formed from relatively short fibers, such as woodpulp fibers. The minimum length of the fibers depends on the methodselected for forming the nonwoven fabric. Where the nonwoven fabric isformed by the wet or dry method, the fiber length is desirably fromabout 0.1 millimeters to 15 millimeters. Desirably, the nonwoven fabricof the present invention has a relatively low wet cohesive strength whenit is not bonded together by an adhesive or binder material. When suchnonwoven fabrics are bonded together by an adhesive, which loses itsbonding strength in tap water and in sewer water, the fabric will breakup readily by the agitation provided by flushing and moving, through thesewer pipes.

The finished wipes may be individually packaged, preferably in a foldedcondition, in a moisture proof envelope or packaged in containersholding any desired number of sheets in a water-tight package with awetting agent applied to the wipe. Relative to the weight of the dryfabric, the wipe may contain from about 10 percent to about 400 percentand desirably from about 100 percent to about 300 percent of the wettingagent. The wipe must maintain its desired characteristics over the timeperiods involved in warehousing, transportation, retail display andstorage by the consumer. Accordingly, shelf life may range from twomonths to two years.

Various forms of impermeable envelopes for containing wet-packagedmaterials such as wipes and towelettes and the like are well known inthe art. Any of these may be employed in packaging the premoistenedwipes of the present invention.

In one embodiment of the present invention, wet wipes, comprising theabove-described nonwoven fabric, are stored in an impermeable packageand saturated with a salt solution containing greater than about 0.5weight percent of one or more monovalent salts, such as NaCl or KCl.Desirably, the salt solution contains about 0.5 to 3.0 weight percent ofone or more monovalent salts. In another embodiment, the wet wipes aresaturated with a salt solution containing greater than about 500 ppm ofone or more multivalent ions, such as Ca²⁺ or Mg²⁺ ions. In a furtherembodiment, the wet wipes are saturated with a salt solution containinggreater than about 0.5 weight percent of one or more monovalent salts incombination with one or more multivalent ions, wherein the concentrationof multivalent ions is greater than about 500 ppm. Desirably, the wetwipes possess an in-use tensile strength of at least 100 g/in, and atensile strength of less than about 30 g/in after being soaked in waterhaving a concentration of Ca²⁺ and/or Mg²⁺ ions of about 50 ppm forabout one hour. More desirably, the wet wipes possess an in-use tensilestrength of at least 300 g/in, and a tensile strength of less than about30 g/in after being soaked in water having a concentration of Ca²⁺and/or Mg²⁺ ions of about 50 ppm for about one hour. In a furtherembodiment, the wet wipes desirably possess an in-use tensile strengthof at least 200 g/in, and a tensile strength of less than about 20 g/inafter being soaked in water having a concentration of Ca²⁺ and/or Mg²⁺ions of about 200 ppm for about one hour. Even more desirably, the wetwipes possess an in-use tensile strength of at least 300 g/in, and atensile strength of less than about 20 g/in after being soaked in waterhaving a concentration of Ca²⁺ and/or Mg²⁺ ions of about 200 ppm forabout one hour.

The nonwoven fabrics of the present invention may also be incorporatedinto such body fluid absorbing products as sanitary napkins, diapers,surgical dressings, tissues and the like. The binder is such that itwill not dissolve when contacted by body fluids since the concentrationof ions in the body fluids is above the level needed for dissolution.The nonwoven fabric retains its structure, softness and exhibits atoughness satisfactory for practical use. However, when brought intocontact with water having a concentration of multivalent ions, such asCa²⁺ and Mg²⁺ ions, of up to about 200 ppm, the binder disperses. Thenonwoven fabric structure is then easily broken and dispersed in thewater.

In one embodiment of the present invention, the in-use tensile strengthof a nonwoven fabric is enhanced by forming the nonwoven fabric with abinder material comprising an ion sensitive polymer of the presentinvention and subsequently applying one or more monovalent and/ormultivalent salts to the nonwoven fabric. The salt may be applied to thenonwoven fabric by any method known to those of ordinary skill in theart including, but not limited to, applying a solid powder onto thefabric and spraying a salt solution onto the fabric. The amount of saltmay vary depending on a particular application. However, the amount ofsalt applied to the fabric is typically from about 0.1 wt % to about 10wt % salt solids based on the total weight of the fabric. Thesalt-containing fabrics of the present invention may be used in avariety of fabric applications including, but not limited to, femininepads and diapers.

Those skilled in the art will readily understand that the binderformulations and fibrous substrates of the present invention may beadvantageously employed in the preparation of a wide variety ofproducts, including but not limited to, absorbent personal care productsdesigned to be contacted with body fluids. Such products may onlycomprise a single layer of the fibrous substrate or may comprise acombination of elements as described above. Although the binderformulations and fibrous substrates of the present invention areparticularly suited for personal care products, the binder formulationsand fibrous substrates may be advantageously employed in a wide varietyof consumer products.

The present invention is further illustrated by the following examples,which are not to be construed in any way as imposing limitations uponthe scope thereof. On the contrary, it is to be clearly understood thatresort may be had to various other embodiments, modifications, andequivalents thereof which, after reading the description herein, maysuggest themselves to those skilled in the art without departing fromthe spirit of the present invention and/or the scope of the appendedclaims.

EXAMPLE 1 Preparation of Ion-Sensitive Polymers

Acrylic acid (43.3 g, 0.60 mol), AMPS (10.7 g, 0.052 mol), butylacrylate (35.2 g, 0.27 mol), and 2-ethylhexyl acrylate (20 g, 0.11 mol)were dissolved in 55 g of acetone/water (70/30) mixture. An initiator,2,2-azobisisobutyronitrile (AIBN) (0.51 g, 3.1×10⁻³ mol), was dissolvedin 20 ml of acetone. The monomer solution was deoxygenated by bubblingN₂ through the solution for 20 minutes. To a 1000 ml three-neck roundbottom flask, equipped with a condenser, two addition funnels and amagnetic stirrer, was added 120 g of an acetone/water (70/30) mixture.The solvent was heated to gentle reflux under nitrogen. Monomers andinitiator were added simultaneously from the addition funnels over aperiod of two hours. Polymerization was allowed to proceed for anadditional two hours, at the end of which, the addition funnels andcondenser were replaced with a distillation head and a mechanical stirrod to remove acetone. A steady stream of N₂ was kept duringdistillation while the temperature was increased gradually from about65° C. to about 90° C. When the distillation was completed, 400 g ofdeionized water was added to reduce the viscosity of the polymersolution A hazy, but uniform solution was obtained.

A total of twelve polymers (Samples 1-12) were synthesized using theabove-described procedure. NaOH (2.1 g, 0.052 mol) in 20 ml of water wasadded at room temperature to neutralize the AMPS component in Samples3-7 and 9-12. The compositions of Samples 1-12 are summarized in Table 1below. All percentages are given in mole percent.

TABLE 1 Ion-Sensitive Polymer Compositions Sample % AMPS % NaAMPS % AA %BA % EHA 1 1.5 0.0 65.5 22.5 10.5 2 3.0 0.0 64.0 22.5 10.5 3 0.0 3.064.0 22.5 10.5 4 0.0 3.5 63.5 22.5 10.5 5 0.0 3.9 62.1 24.6 9.4 6 0.04.0 57.0 26.5 12.5 7 0.0 4.2 64.7 19.7 11.4 8 5.0 0.0 62.0 22.5 10.5 90.0 5.0 58.0 26.5 10.5 10 0.0 4.0 63.0 21.5 11.5 11 0.0 5.0 59.0 25.510.5 12 0.0 5.0 60.0 24.5 10.5

COMPARATIVE EXAMPLE 1 Comparative Testing of a Polymer Supplied fromLion Corporation

A Lion polymer was supplied from Lion Corporation and tested as outlinedin the examples below. The polymer was one of the polymers disclosed andclaimed in U.S. Pat. No. 5,312,883, assigned to Lion Corporation.

COMPARATIVE EXAMPLE 2 Preparation of a Lion Corporation Polymer

A Lion polymer was produced using the polymerization procedure outlinedin Example 2 of U.S. Pat. No. 5,312,883. The following monomers wereused: acrylic acid (50 g, 0.69 mol), butyl acrylate (25 g, 0.20 mol),and 2-ethylhexyl acrylate (25 g, 0.14 mol). The polymer was neutralizedwith 0.1 mol sodium hydroxide.

EXAMPLE 2 Improved Hard Water Sensitivity of Unneutralized PolymerCompared to the Lion Polymers

The sensitivity of the unneutralized polymers of Example 1 and the Lionpolymers of Comparative Examples 1 and 2 to divalent cations present inhard water was measured. Samples 1, 2, and 8 of Example 1 and the Lionpolymer were placed in a number of CaCl₂ solutions with a Ca²⁺concentration varying from 100 to 1000 ppm. Following soaking for anhour, the solubility of each polymer was noted. The solubility resultsare given below in Table 2.

TABLE 2 Solubility Results Solubility in Ca²⁺ Sample 100 ppm 200 ppm 300ppm 1000 ppm Sample 1 1 2 3 5 Sample 2 1 2 2 5 Sample 8 1 1 1 5 Comp.Ex. 1 4 5 5 5 Comp. Ex. 2 2 4 4 5 Note: 1: very light cloudiness; 2:light cloudiness; 3: moderate cloudiness (cloudy, but light still ableto penetrate through solution); 4: severe cloudiness (milky); 5: heavyprecipitation (solid gel formation).

The results of Table 2 indicate that the AMPS-containing polymers weremuch less sensitive to Ca²⁺ ion concentration relative to the Lionpolymers. However, with a sufficient amount of Ca2+ ion present (about1000 ppm), all of the polymers will “salt out” of the solution. In otherwords, all of the polymers will be insoluble in the 1000 ppm Ca²⁺ ionsolution.

A further dissolution experiment supported these results. The fiveprecipitates were then removed from the 1000 ppm Ca²⁺ solutions andplaced in deionized water. Samples 1, 2 and 8, which contained AMPS,redissolved in the deionized water; however, the Lion polymers (fromComparative Examples 1-2) did not due to irreversible crosslinking ofthe sodium acrylate sites.

Reduction in the ion sensitivity of AMPS-containing polymers towardmultivalent ions was found to be not limited to Ca²⁺ ions. In a separateexperiment, Samples 2 and 8 along with the Lion polymers of ComparativeExamples 1-2 were precipitated in a ZnCl₂ solution having a Zn²⁺ ionconcentration of 5000 ppm. The precipitates of Sample 2 and 8redissolved in water, but the Lion polymers did not. This suggestedthat, in general, the AMPS-containing polymers were less sensitivetoward divalent cations and did not form a permanent cross-linkingstructure.

EXAMPLE 3 Testing the Binding Strength of the AMPS-Containing PolymersCompared to the Lion Polymer

The binding strength of the AMPS-containing polymers was tested in 100and 200 ppm Ca²⁺ solutions. The five polymers (Samples 1, 2 and 8 andthe Lion polymers of Comparative Examples 1 and 2) were applied via a#20 wire-wound rod to five identical water-dispersible, wet-laidnon-woven webs composed of BFF rayon fibers (1.5 d×25 mm). The fabricsamples were dried in a forced-air oven at 50° C. The add-on level wasbetween about 55 and 61 wt % based on the total weight of the fabric.The non-woven sheets were cut to provide 1 inch×3 inch strips from eachsheet. The dry samples were put directly into Ca²⁺ ion solutions. Thestrips were tested for tensile strength after soaking in solution for anhour according to the following test method.

The strips were mounted onto a minitensile tester with a 2″ gripseparation. The strength was tested at a speed of 18 cm/min and themaximum peak load was recorded. The results are summarized in Table 3below.

TABLE 3 Tensile Strength Strength (g/in) in Ca²⁺ (ppm) Solutions Sample100 ppm 200 ppm Sample 1 0 360 Sample 2 0 361 Sample 8 0 0 Comp. Ex. 1292 529 Comp. Ex. 2 281 567

The results of Table 3 again illustrate the reduced sensitivity ofAMPS-containing polymers toward Ca²⁺ ions. Binders composed of Sample 1and 2 were dispersible in 100 ppm Ca²⁺ solutions and a binder composedof Sample 8 was dispersible in solution containing up to 200 ppm Ca²⁺.These polymers showed a significant improvement over the Lion polymers.

EXAMPLE 4 Adjusting the pH of Solutions Containing the Ion-sensitivePolymers

The solution pH of Samples 1, 2 and 8 of Example 1 were found to bequite low, ranging from 1.7 for Sample 8 to 2.1 for Sample 1, due to thepresence of sulfonic acid groups. Low pH is undesirable in applicationssuch as wet wipes, not only because it causes yellowing of the pulpsubstrate in the drying process, but it may irritate the skin duringuse. To adjust the pH of these solutions, equimolar amounts of NaOH wereadded to neutralize the AMPS. The pH of the solutions rose to about3.1-3.3, a more desirable pH range for skin health, which alsoeliminates yellowing of the fibrous substrate during drying.

EXAMPLE 5 Effect of Neutralization on the Dispersion Rate ofIon-sensitive Polymers

Five polymer solutions containing three polymers of Example 1 (Samples1-3) and the Lion polymers of Comparative Examples 1-2 were applied viaa #20 wire-wound rod to five identical water-dispersible, wet-laidnon-woven webs composed of BFF rayon fibers (1.5 d×25 mm). The fabricsamples were dried in a forced-air oven at 50° C. The add-on level wasbetween about 55 and 61 wt % based on the total weight of the fabric.The non-woven sheets were cut to provide 1 inch×3 inch strips from eachsheet.

The strips were placed in deionized water. The time of dispersion (i.e.,the time at which each fabric sample had substantially zero tensilestrength) was recorded. Results are given in Table 4 below.

TABLE 4 Time of Dispersion in Deionized Water Fabric Sample Time toDisperse 1 >2 hours 2 >2 hours 3 ˜10 minutes Comp. Ex. 1  ˜3 minutesComp. Ex. 2  ˜3 minutes

As shown in Table 4, the strips containing Lion polymer lost all oftheir strength in about three minutes, indicating good dispersibility indeionized water. The strips formed from the AMPS-containing polymers hadpoor dispersibility in deionized water. However, the strips formed fromthe NaAMPS-containing polymer had good dispersibility in deionizedwater.

In order to determine the effect of Ca²⁺ ion concentration on thedispersibility of Sample 3, strips of Sample 3 were tested for tensilestrength after soaking for up to one hour in solutions containing from 0to 200 ppm Ca²⁺ ion. The sample was found to be stable in a 0.9 wt %NaCl solution, and dispersable in deionized water in less than 10minutes. In a 200 ppm Ca²⁺ solution, the strip had an initial strengthof about 275 g/in. In a 100 ppm Ca²⁺ solution, the strip had thestrength of less than about 50 g/in after one hour and becameunrecognizable after two hours. It was concluded that whileneutralization increased the dispersion rate significantly, it did notnegatively alter the strength characteristics and Ca²⁺ sensitivity ofthe ion-sensitive polymers of the present invention.

EXAMPLE 6 Water-Dispersibility Testing of Nonwoven Fabrics

Ten polymer solutions containing eight polymers of Example 1 (Samples 1and 3-9) and the Lion polymers of Comparative Examples 1-2 were appliedvia a #20 wire-wound rod to ten identical water-dispersible, wet-laidnon-woven webs composed of BFF rayon fibers (1.5 d×25 mm). The fabricsamples were dried in a forced-air oven at 50° C. The add-on level wasbetween about 55 and 61 wt % based on the total weight of the fabric.The non-woven sheets were cut to provide 1 inch×3 inch strips from eachsheet. The strips were tested for water-dispersibility according to thefollowing procedure.

The 1 inch×3 inch strips from the ten nonwoven sheets were soaked insolutions having a Ca²⁺ ion concentration from 100 to 1000 ppm for aboutone hour. The samples were removed from the solutions and tested fortensile strength in the machine direction using the procedure outlinedabove. Samples having a low tensile strength showed goodwater-dispersibility. Test results are given below in Table 5.

TABLE 5 Tensile Strength of Ion-Sensitive Polymers in Ca²⁺ Ion Solutions(ppm Ca²⁺ Ion) (g/in) Fabric Sample 100 ppm 200 ppm 500 ppm 1000 ppm 1 0360 3 0 275 498 4 0 39 471 445 5 0 327 522 441 6 310 482 529 7 0 0 301335 8 0 0 9 0 21 510 503 Comp. Ex. 1 292 529 Comp. Ex. 2 281 567 813 799

As shown in Table 5, the tensile strength of the nonwoven fabrics formedfrom the AMPS-containing or NaAMPS-containing polymers, in most cases,decreased as the concentration of Ca²⁺ ion decreased. By controlling thehydrophobic/hydrophilic balance in the composition of the polymericbinder, nonwoven fabrics were produced having good water-dispersibilityas identified by a low tensile strength in solutions having a Ca²⁺ ionconcentration of 100 or 200 ppm (see Samples of Polymer 4, 7, 8, and 9above).

In contrast, the water-dispersibility or ion-triggerability of the Lionpolymers was found to be unacceptable for flushable applications. Thenonwoven fabrics formed from the Lion polymers had an extremely hightensile strength (>281 g/in) in solutions having a Ca²⁺ ionconcentration of 100 or 200 ppm. Given these results, nonwoven fabricsformed from the Lion polymers would not be suitable in flushableproducts in areas of hard water.

EXAMPLE 7 Variation of the Composition of NaAMPS-Containing Polymers toAffect Tensile Strength in NaCl Solutions and Dispersibility in Ca²⁺Solutions

Ten nonwoven fabrics comprising binder materials formed from eightpolymers of Example 1 (Samples 4-7 and 9-12) and the Lion polymers ofComparative Examples 1-2 were prepared as in Example 7. In-use strengthand dispersibility of the NaAMPS-containing fabrics and the Lionpolymer-containing fabrics were measured as described above.

The 1 inch×3 inch strips from the ten nonwoven sheets were tested on amachine using the test method described above. In-use strength of thepolymeric binder was measured as the tensile strength in the machinedirection of each sample tested in a 0.9 wt % NaCl salt solution or a1.5 wt % NaCl salt solution after soaking overnight at room temperature,unless otherwise indicated.

To determine the dispersibility of some of the pre-soaked samples, thesample was transferred after soaking in one of the above salt solutionsto a solution containing a Ca²⁺ ion concentration from 100 to 200 ppmCa²⁺ for an hour, and tested for tensile strength. Samples having a lowtensile strength showed good water-dispersibility. Test results aregiven below in Table 6.

TABLE 6 Tensile Strength of Ion-Sensitive Polymers in Ca²⁺ Ion Solutions(ppm Ca²⁺ Ion) and NaCl Solutions (g/in) Fabric 0.9 wt % 1.5 wt % 100ppm 150 ppm 200 ppm Sample NaCl NaCl Ca²⁺ Ca²⁺ Ca²⁺  4* 0 364 0 39  5* 0350 0 327  6* 315 310 482  7* 0 322 0 0  9** 0 449 62 10** 0 378 52 15511** 442 0 12** 386 0 Comp. 529 292 529 Ex. 1* Comp. 375 645 699 698 Ex.2** Note: *Samples were tested after 1 hour soaking in the designatedsolution. **Dry samples were pre-soaked overnight in a NaCl solution,then put directly into a Ca²⁺ solution, and tested after 1 hour.

As shown in Table 6, the fabric samples formed from NaAMPS-containingpolymers had very little tensile strength in 0.9 wt % NaCl solution. Incontrast, fabric samples formed from the Lion polymers had high tensilestrength. In the 1.5 wt % NaCl solution, fabric samples formed fromNaAMPS-containing polymers had good tensile strength. The increase intensile strength may be attributed to an increase in the salting-outeffect of the NaAMPS-containing polymers.

Further, Table 6 shows that most of the fabric samples formed fromNaAMPS-containing polymers lost all or a significant portion of theirtensile strength after soaking in a 100 ppm Ca²⁺ ion solution. Also,fabric samples 11 and 12 lost their tensile strength after beingtransferred to and soaking in a 200 ppm Ca²⁺ ion solution, indicatinggood water dispersibility. In contrast, fabric samples formed from theLion polymers did not lose their tensile strength in 100 ppm or 200 ppmCa²⁺ ion solutions, indicating poor dispersibility.

EXAMPLE 8 Effect of Divalent Ion Salts on the In-Use Tensile Strengthand Water-Dispersibility of Nonwoven Fabrics Bound withNaAMPS-Containing Polymers

Example 7 indicates that NaAMPS-containing polymers, that aredispersible in 200 ppm Ca²⁺ solution, have acceptable in-use tensilestrength only in higher NaCl concentrations (greater than 0.9 wt %NaCl). In order to possibly increase the tensile strength of thesebinders at a lower NaCl concentration, salts containing divalent cationssuch as Ca²⁺ and Zn²⁺ were added to the NaCl solutions because of theirhigher salting-out capability. Samples 3-7 and 9 of Example 1 were usedas binder material for nonwoven fabrics comprising BFF rayon fibers asdescribed above. Tensile strength of the fabrics was measured aftersoaking in a variety of solutions. Results of the testing are summarizedin Table 7 below.

TABLE 7 Tensile Strength of Ion-Sensitive Polymers in Mixed SaltsSolutions (g/in) 500 1000 0.9% NaCl 0.9% NaCl 0.9% NaCl Fabric ppm ppmwith 500 with 1000 with 500 Sample Ca²⁺ Ca²⁺ ppm Ca²⁺ ppm Ca²⁺ ppmZ{overscore (n)}²⁺ 3 498 498 4 471 445 420 335 5 522 441 432 6 529 573 7301 335 379 335 304 9 0 503 585 461 379

The results of Table 7 indicate that the NaAMPS-containing polymers arestable in all test solutions, demonstrating the effectiveness ofdivalent ions in stabilizing the polymer, even at low NaClconcentrations. In some cases, the polymers may be stabilized with thedivalent ion salt alone. As further shown in Table 7 in comparison withTable 6, Ca²⁺ ions are more effective at stabilizing the polymers thanNa⁺ ions or Zn²⁺ ions, as demonstrated by the higher tensile strengthvalues in the NaCl solutions containing Ca²⁺ ions as opposed to the NaClsolutions containing Zn²⁺ ions in the comparable concentration level.

EXAMPLE 9 Solubility of Ion-Triggerable Polymers as Measured byPercentage Weight Loss in a Divalent Ion Salt Solution

Films were produced from three polymers of Example 1 (Samples 9, 10, and12) and the Lion polymer of Comparative Example 1. Weighed samples ofeach film were placed in a 1.5 wt % NaCl solution for 24 hours. Thesamples were removed and weighed to determine the percent weight loss ofeach sample. Similarly, weighed samples of each film were placed in asolution containing 200 ppm Ca²⁺/Mg²⁺ ions (2 parts Ca²⁺ to 1 part Mg²⁺)and agitated by shaking for about 2 hours. The samples were removed andweighed to determine the percent weight loss of each sample.

TABLE 8 Percent Weight Loss of Films of Ion-Sensitive Polymers in SaltsSolutions % Wt. Loss in 1.5% % Wt. Loss in 200 Sample NaCl ppm Ca²⁺/Mg²⁺ 9 0 38 10 0 34 12 0 100 Comp. Ex. 1 0 5

All five samples show 0% weight loss after being soaked in 1.5% NaCl for24 hours, indicating that all samples were substantially insoluble inthe NaCl solution. In the Ca²⁺/Mg²⁺ solution, the Lion polymer had verylittle weight loss, indicating that the Lion polymer was substantiallyinsoluble in the solution. However, the polymers of the presentinvention had a weight loss of at least 34% in the Ca²⁺/Mg²⁺ solution,indicating that the samples formed from the ion-triggerable polymers ofthe present invention were soluble in the solution. Moreover, Sample 12had a weight loss of 100%, indicating substantial solubility in theCa²⁺/Mg²⁺ solution.

The results of Table 8 further confirm the results of Example 6. Inparticular, the water-dispersibility or ion-triggerability of the Lionpolymer was found to be unacceptable for flushable applications,especially flushable applications in areas of hard water. However, thewater-dispersibility or ion-triggerability of the polymers of thepresent invention was found to be acceptable for flushable applications,including flushable applications in areas of hard water.

The above disclosed examples are preferred embodiments and are notintended to limit the scope of the present invention in any way. Variousmodifications and other embodiments and uses of the disclosedwater-dispersible polymers, apparent to those of ordinary skill in theart, are also considered to be within the scope of the presentinvention.

1. A nonwoven fabric, comprising: fibrous material, and a bindermaterial comprising a binder composition comprising an ion-sensitivepolymer comprising a first repeat unit derived from a monomer selectedfrom styrenesulfonic acid (SS), a sodium salt of styrenesulfonic acid(NaSS), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), a sodiumsalt of 2-acrylamido-2-methyl-1-propanesulfonic acid (NaAMPS),vinylsulfonic acid, a sodium salt of vinylsulfonic acid, andcombinations thereof; a second repeat unit derived from a monomerselected from acrylic acid, a sodium salt of acrylic acid, methacrylicacid, a sodium salt of methacrylic acid, and combinations thereof; and athird repeat unit derived from a monomer selected from at least onealkyl acrylate, at least one alkyl methacrylate, and combinationthereof; wherein the fabric is not substantially water-dispersible in aneutral salt solution containing at least about 0.3 weight percent salt,said salt comprising one or more monovalent or multivalent ions; and thefabric is substantially water-dispersible in tap water containing one ormore multivalent ions.
 2. A method of making an ion-sensitive polymer,comprising: forming a hydrophilically/hydrophobically balanced mixtureof three or more monomers, wherein at least one monomer contains one ormore hydrophilic moieties, and at least one monomer contains one or morehydrophobic moieties, and wherein the mixture comprises: AMPS or NaAMPS,acrylic acid, butyl acrylate, and 2-ethylhexyl acrylate; andpolymerizing the mixture; wherein the polymer is insoluble in neutralsalt solution containing at least about 0.3 weight percent salt, saidsalt comprising one or more monovalent or multivalent ions; and whereinthe polymer is soluble in tap water containing one or more multivalentions.
 3. A nonwoven product comprising: at least about 50 weight percentfibers from about 0.1 to 15 m in length, and from about 5 to about 50weight percent of a binder composition comprising an ion-sensitivepolymer comprising a first repeat unit derived from a monomer selectedfrom styrenesulfonic acid (SS), a sodium salt of styrenesulfonic acid(NaSS), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), a sodiumsalt f 2-acrylamido-2-methyl-1-propanesulfonic acid (NaAMPS),vinylsulfonic acid, a sodium salt of vinylsulfonic acid, andcombinations thereof; a second repeat unit derived from a monomerselected from acrylic acid, a sodium salt of acrylic acid, methacrylicacid, a sodium salt o methacrylic acid, and combinations thereof; and athird repeat unit derived from a monomer selected from at least onealkyl acrylate, at least one alkyl methacrylate, and combinationthereof; wherein the product is not substantially water-dispersible in asalt solution having a multivalent ion concentration greater than about500 ppm, further wherein the product is water-dispersible in a saltsolution having a multivalent ion concentration less than about 200 ppm.4. The nonwoven product of claim 3, wherein the binder compositioncomprises from about 10 to about 35 weight percent.
 5. The nonwovenproduct of claim 3, wherein the binder composition comprises from about10 to about 25 weight percent.
 6. The nonwoven product of claim 3,wherein the fibers are about 0.2 to 6 mm in length.
 7. The nonwovenproduct of claim 3, further wherein the product has an in-use tensilestrength of about 100 g/in, and a tensile strength of less than about 30g/in after being soaked in water having a concentration of Ca²⁻ and/orMg²⁺ ions of about 50 ppm for about one hour.
 8. The nonwoven product ofclaim 3, further wherein the product has an in-use tensile strength ofabout 300 g/in, and a tensile strength of less than about 30 g/in afterbeing soaked in water having a concentration of Ca²⁺ and/or Mg²⁺ ions ofabout 50 ppm for about one hour.
 9. The nonwoven product of claim 3,further wherein the product has an in-use tensile strength of about 200g/in, and a tensile strength of less than about 20 g/in after beingsoaked in water having a concentration of Ca²⁺ and/or Mg²⁺ ions of about200 ppm for about one hour.
 10. The nonwoven product of claim 3, furtherwherein the product has an in-use tensile strength of about 300 g/in,and a tensile strength of less than about 20 g/in after being soaked inwater having a concentration of Ca²⁺ and/or Mg²⁺ ions of about 200 ppmfor about one hour.
 11. A method of making an ion-sensitive polymer,comprising: forming a hydrophilically/hydrophobically balanced mixtureof three or more monomers, wherein at least one monomer contains one ormore hydrophilic moieties, and at least one monomer contains one or morehydrophobic moieties; wherein the monomer mixture comprises: a firstmonomer selected from styrenesulfonic acid (SS), a sodium salt ofstyrenesulfonic acid (NaSS), 2-acrylamido-2-methyl-1-propanesulfonicacid (AMPS), a sodium salt of 2-acrylamido-2-methyl-1-propanesulfonicacid (NaAMPS), vinylsulfonic acid, a sodium salt of vinylsulfonic acid,and combinations thereof; a second monomer selected from acrylic acid, asodium salt of acrylic acid, methacrylic acid, a sodium salt ofmethacrylic acid, and combinations thereof; a third monomer selectedfrom at least one alkyl acrylate, at least one alkyl methacrylate, andcombinations thereof; and polymerizing the mixture; wherein the polymeris substantially insoluble in a neutral salt solution containing atleast about 0.3 weight percent salt, said salt comprising one or moremonovalent or multivalent ions; and wherein the polymer is substantiallysoluble in tap water containing one or more multivalent ions.
 12. Thenonwoven fabric of claim 1, wherein the fabric is not substantiallywater-dispersible in a neutral salt solution containing from about 0.5weight percent to about 5.0 weight percent of the salt.
 13. The nonwovenfabric of claim 1, wherein the fabric is not substantiallywater-dispersible in a neutral salt solution containing from about 1.5weight percent to about 5.0 weight percent of the salt.
 14. The nonwovenfabric of claim 1, wherein the multivalent ions comprise Ca²⁺ ions, Mg²⁺ions, Zn²⁺ ions, or a combination thereof.
 15. The nonwoven fabric ofclaim 1, wherein the monovalent ions comprise Na⁺ ions, Li⁺ ions, K⁺ions, NH₄ ⁺ ions, or a combination thereof.
 16. The nonwoven fabric ofclaim 1, wherein the polymer comprises repeat units derived from AMPS orNaAMPS; acrylic acid, methacrylic acid or a combination thereof; and oneor more alkyl acrylates.
 17. The nonwoven fabric of claim 16, whereinthe polymer comprises repeat units derived from AMPS or NaAMPS, acrylicacid butyl acrylate, and 2-ethylhexyl acrylate.
 18. The nonwoven fabricof claim 17, wherein the polymer comprises from greater than 0 to about10 mol % repeat units derived from AMPS or NaAMPS; from about 50 to lessthan 67 mol % repeat units derived from acrylic acid; from about 15 toabout 28 mol % repeat units derived from butyl acrylate; and from a to 7to about 15 mol % repeat units derived from 2-ethylhexyl acrylate. 19.The nonwoven fabric of claim 18, wherein the polymer comprises fromabout 1 to about 6 mol % repeat units derived from AMPS or NaAMPS; fromabout 57 to less than 66 mol % repeat units derived from acrylic acid;from about 15 to about 28 mol % repeat units derived from butylacrylate; and from about 7 to about 13 mol % repeat units derived from2-ethylhexyl acrylate.
 20. The nonwoven fabric of claim 1, wherein thefabric is substantially water-dispersible in tap water containing fromabout 15 ppm to about 500 ppm of one or more multivalent ions.